Flux shifting trip magnet for circuit breaker



Sept. 22, 1959 c. l. cLAuslNG ETAL 2,905,865

FLUX SHIFTING TRIP MAGNET FOR CIRCUIT BREAKER Filed Dec. 19, 1956 l A 2Sheets-Sheet 1.

Ami/@ff Sept 22, 1959 c. l. CLAUSING ETAL 2,905,865

FLUX sHIFTING TRIP MAGNET RoR CIRCUIT BREAKER Filed Dec. 19, 195e 2Shets-Sheet 2 Til@ E;

f/gg /32 BY h? WM United States Patent C) FLUX SHIFTING TRIP MAGNET FORCIRCUIT BREAKER Challiss I. Clausing, Collingswood, NJ., and Frank J.Pokorny, Hatboro, Pa., assignors to I-T-E Circuit Breaker Company,Philadelphia, Pa., a corporation of Pennsylvania Application December19, 1956, Serial No. 629,392

11 Claims. (Cl. 317-43) Our invention relates to a flux shifting type ofmagnet which serves the dual function of a high speed reverse currenttrip unit and a magnetic latch for high speed D.C. breakers.

The type of magnetic latch to which our novel invention is directed isset forth in U.S. Patent No. 2,412,- 247 to D. I. Bohn land assigned tothe assignee of the instant invention. As set forth in the abovereference, the movable contact structure of a D.C. circuit breaker ismaintained in engagement with its cooperating stationary contacts bymeans of a magnetic armature which is sealed to a closing magneticstructure. This closing magnetic structure is comprised of a polarizingcoil for creating a unidirectional liux in the magnetic core and linkingthe armature, and a bucking bar which carries at least a portion of theD.C. load current -and serves to create a linx which adds to thearmature liux created by the polarizing coil when D.C. current is beingcarried in the normal forward direction.

In the event of a reversal of the liow of D.C. current, the currentthrough the bucking bar reverses in direction, and its associatedmagnetic liux reverses and serves to buck down or shift the linx of thepolarizing coil through the armature so as to reduce the magneticlinkage between the magnetic armature and the closing magneticstructure. The movable contact may then be moved to a disengagedposition to open the circuit by biasing means once the magnetic latch isdefeated as noted above.

This type of trip unit 'and magnetic latch has had wide application inD.C. breakers of high current low Voltage rectifying systems. When aplurality of rectifiers are connected in parallel, it is important thata back-firing rectifier or a rectifier which is short circuited so as toallow reverse current to liow therethrough is taken off the line as soonas possible, and that the total load current be redistributed betweenthe remaining unfaulted rectilier units.

It has been found, however, that the above described magnetic trip unitof the breakers associated with the unfaulted rectiliers operate torelease their armatures when current in the forward direction increasesfrom a first value to a second higher value in a short time, thiscondition being obtained when the load current of a faulted unit isredistributed between the remaining units.

It has further been found that the magnetic armature is released whenforward current is rapidly decreased from an excessively high value to alower value, this condition occurring when one or more rectifier unitsare connected in parallel with other rectifier units which are alreadycarrying a forward load current.

Also, this condition occurs when a backfire current is suddenly clearedin one rectifier unit and the forward current contribution of the units,thus suddenly removed. This condition prevails when the magnetic tripunit has not released on the initial rise of forward fault currentcontribution described above.

Clearly, it is desirable, and in some cases essential,

ICC

as in certain electrolytic applications, that the remaining unitscarrying load current are not taken olir the line due to a rapidincrease or decrease in their load currents.-

This is highly undesirable since the service of many rectifiers may belost when only one is faulted, or 'another rectifier is cut intoparallel operating service.

One explanation for the above type operation is that extraneous magneticfields generated by current fiowing in other parts of the circuitbreaker and in the external bus work tend to distort or cancel thedesired flux linkages between the closing magnet and its cooperatingarmature.

In the first case Where the breaker trips due to the application ofincreased forward current of sufficient magnitude and rate of rise, itis possible that external fields are applied in the same generaldirection as the flux linking the armature and closing structure todistort the total linx linkages and cause release of the armature. Whenthe external field is applied in an opposite direction as the originalarmature field there is, of course, a reduction in linking liux due tocancellation and once again the armature is released.

In the second case where the breaker is operated due to a sudden removalof a portion of the forward current and an external field is applied ina direction opposite that of the core linx, there will be a cancellationof flux and possible operation of the armature.

When, on the other hand, the external field is in a direction to createmagnet-armature linkages of its own which would hold the breaker closed,then upon removal of this excessive external field there will be a timelag before polarizing flux builds up, and during this period the liuxlinkages may be reduced to a tripping point where the armature isreleased.

The principal object of our invention is to provide a magnetic structurewherein the magnet and its armature are free of the effects due toexternal fluxes.

More specifically, we provide a feed-back type of control Which utilizesa transformer means operable responsive to change in forward current,which induces compensating magnet-armature linking linx responsive to achange in the forward current.

In each case, our novel feed-back or transformer compensating meanscarries at least a portion of the load current of the D.C. breaker in aprimary winding, land the secondary winding output is determined byvariations in this D.C. load current. This secondary winding output isthen connected to the magnetic structure to induce a compensating linxin this magnetic structure so that variations in the liux linking thearmature and the magnet due to variations in the bucking bar current arecompensated. Thus, when the bucking bar current is rapidly increased, aswould be the case when the device is used as the D.C. breaker of arectifier system of parallel connected rectifiers and one of therectifiers backlircs, the current increase in the bucking bar and iiuxincrease associated therewith is compensated for by the novel feed-backtransformer means.

if desired, the output of our novel transformer means could be rectifiedso that compensating linx will be activated within the core only whenthe change in current in the bucking bar is in a predetermineddirection. By way of example, if it is desired to only compensate themagnet so that the armature will remain sealed during the rapid increasein current from a predetermined value, then the transformer secondaryoutput will be rectified so y that a compensating pulse will be passedto the magnet high value to a second and lower value, the compensatingdevice will induce'a blocking ux in the magnet which would tend to causea release of the armature.

If, however, the device is to operate in an application where thiscondition is not likely to appear, this creation of-a blocking fiuXresponsive to a decrease in bucking bar current may be desirable, sinceduring a reverse current fault it, will aidthe reversal'of bucking barflux to oppose the ux due to the polarizing coil and thereby allow amore rapid' disengagement of the armature with respect to the magneticstructure.

Our novel compensating means could also be applied where the D;C.breaker current may be decreased from excessively high currents to somelower currents, this compensation being achieved by reversing therectifying means ofthe secondary transformer winding. Thus, acompensating fiux will now appear only when the buckingbar currentdecreases, but will not appear during anincrease inV bucking bar currentdue to the rectifying means-in the transformer output.

Clearly, each ofthe above conditions co-uld be simulT taneouslycompensated forby providing av first and second feed-back transformermeans of the above described type wherein the rst transformer output isso rectified as to produce a` compensating fiuX for an increasingrectitier current, while the second transformer output is so rectifiedthat a compensating pulse appears only during adecrease in bucking barcurrent.

While the aboveY described transformer means could be of any desiredtype, we have found it preferable to utilize a pulse type transformer soas to prevent saturation of transformer core-within the predeterminedNlimits of current variation. However, normal types of currenttransformers couldy be used.

We have further found that our novel transformer means could utilizethemagnetic structure of the magnetic latch for its magnetic circuit so asto eliminate a separate and distinct magnetic structure for thetransformer primary and secondary windings. T-his is possible when themagnetic latch structure has the usual high reluctance path interposedbetween the armature leg andthe polarizing coil leg. In this casethe-flux through the polarizing coil and the flux due to the bucking barduring current conduction in the forwardvdirection are in seriesVthrough the` armature leg, but arelinopposingHV relationshipin the highreluctance leg. Thus, when thecurrent'in the bucking bar varies therewill be afluX change in the high re' -luctance leg. By utilizing thebucking'bar as the primary windingfor our novel transformer compensatingmeans, and byV placingpa secondary winding on the high reluctance leg,1t is clear that this. secondary winding will have an output responsiveto variations inthe bucking bar current. This output may then be appliedto` another portion of the magnetic latch structure inthe mannerdescribed heretofore so as to compensate for variations in iiuxlinkagesbetween the magnet and its armature due to variations-in thecurrent through the buckingtbar.

Accordingly, the primary object of our invention is to provide acompensating fiux through the armature of' a D.-C. breaker trip unitresponsive tovariations in the current passing through the breaker.y

Another object of this invention is to provide a novel transformer meanshaving a secondary winding energized-responsive to variations in abucking bar current angl,` to. connect the secondary winding to thearmature magnetic structure for compensating for flux changes due to thebucking bar current.

Another object of this invention is to provide a magnetic structurecompensating means wherein the current through a main current conductingmember alters the linking flux between an armature and the magneticstructure, and the variation in ux due to the varying current iscompensated for by anovel transformer having a primary windingVconnected to conductthe current of the current 'carrying means.

Another object of this invention isto provide a novel compensating meansfor preventing the operation of an armature of a magnetic trip unitresponsive to a rapid increase in current through the main conductingmember.

A still further object of this invention is to provide a noveltransformer compensating means for the magnetic structure of a magnetictrip unitA wherein the main co11- ducting member serves as a primarywinding,and'alsec ondarywinding is woundgin ahigh reluctance leg of themagnetic structure and is connected to induce compensating fluxes inthemagnetic structure` to compensate for variations in the currentvthroughr the main. conducting member.

A still further object of this invention is to provide a noveltransformer compensating meansfor. amagnetio trip unit wherein thesecondary windingis energized responsive to variations of the currentthrough the main conducting member and the output of the secondarywinding is rectified to produce compensationresponsive to'currentchanges in a predetermined direction;

These and other. objects of` my invention will now be apparent from thefollowing description when taken inconnection with` the drawings, in.which:

Figure l schematically shows themanner in which a magnetic trip unit ofthe type towhich our'invention could be applied can. be connected to-a.contact structure of al circuit breaker.

Figure 2 shows a cross'sectional, view ofthe magnetand armature ofFigure. 1y whentaken across the'lines 2 2.

Figure 3 is similar to Figure l and:shows\the armature and contactstructure in a disengagedposition.

Figure 4 schematically represents a plurality of parallel connectedrectifiers. which could have D.C. circuit breakers with magnetic latchtype trip unitsandillus- 'rates the current conditions. with one ofv therectifiers carrying back-feed current;

Figure 5 shows. a plot. o-fvforwardlcurrent versus time for the currentthrough. the Ds-C. breaker contacts of one of the unfaultedrectifiersof.` Figure 4.

Figure 6 illustrates a first. embodimentv ofour novel invention whenapplied to the. magnetic struc-ture of Figure l.

Figure 7 illustrates asecond embodimentoffour'novei invention whereinthe novell transformer compensating means are arrangedttocompensate forbothvincreaseor decrease in forward current. f

Figure 8 illustrates `a further. embodiment ofour' novel invention whenthe, magnetic latch, magneticA structure servesthe purpose ofthecompensating.transformer magnetic structure.

Figure 9 illustrateshow the. device of 'Figure 8 may-be modified so, astocompensate for bothincreaseand' decrease of forward current.

Figure l0 showsa top.crossrsectional'viewoff a second type of magneticstructure which could operateas a magnetic trip unit and'could beprovided with ournovel compensatingv means.

Figure ll shows. a cross-sectional View of FigureA l0 when takenacrosslthelines 11e-11.

Figure 12 showsa cross-sectional view of the armature of Figure l0 whentaken acrossthelnes- 12*12.k

Referringfirst toFigure l which shows a well known typeof magneticstructure inconjunction withits operativeconnection to the circuitbreaker; contacts,l it isseen that the. magnetic latch unit is comprisedof` ama-gnetic structure Zie-and an armature 22 which.ismovable'` intoandroutgof engagement withtthe armature fluX-V path- 24 of magnet 20.Magneticstructure/ 2f), which may. be a laminated structureasshownin-.Figure 2'; is furthercomprised of ahigh reluctance path 26andiapolarizing coil flux p ath 28.

The magnetic structure,- is energized by. a polarizing coil 30whichisenergized at terminals.32 and eby. a D.C. source lso ask tocreateatunidirectional fiuxwhich will. @QW through. the'armature flux path.24? and the armature22 to` thereby maintain armature 22 sealed to themagnetic structure 20.

Magnetic structure 20 is further energized by a second winding orbucking bar 36 which passes between the armature flux path 24 and thehigh reluctance flux path 26. During normal forward current flowindicated by the arrow 38, bucking bar 36, which will hereinafter beinterchangeably described as a current conducting means, will pass aflux through the armature flux leg 24 in the same direction as the fluxcreated by the polarizing coil 30.

Thus, while the bucking bar 36 carries current, the armature 22 will seellux linkages which are given by the sum of the fluxes due to buckingbar 36 and polarizing coil 30.

`In the high reluctance leg 26, however, the fluxes of polarizing coil30 and bucking bar 36 are in opposing or cancelling directions.

The bucking bar 36 is operatively connected to the moving contactstructure 40 of a D.C. circuit breaker by means of the flexibleconducting member 42.

In Figure l it is seen that movable contact structure 40 is inengagement with the cooperating stationary contact structure 44 so as tocomplete a current path from a point 46 of bucking bar 36 to the point48 of the stationary contact structure 44, which points could lead tosubsequent terminal members.

The operative connection between armature 22 and movable contactstructure 40 is shown schematically in Figures l and 3 as being formedby the flexible member 50 which passes over a fixed guide member 52.Thus, in the contact engaged position, the armature 22 is sealed to themagnetic structure 20 and connecting means Sil will maintain contact 40closed against the force of a biasing means 54.

In the event of a reversal of current through bucking bar 36, the fluxdue to bucking bar 36 will reverse and buck down the flux of polarizingcoil 3G in armature path 24 so as to decrease the total linkages betweenmagnetic structure 20 and armature 22. Thus, the force of the openingbias means 54 may then move contact structure 40 to a disengagedposition and remove armature 22 from its sealed or engaged position withrespect to magnetic structure 20, as is shown in Figure 3.

It is to be clearly noted at this point that the connection betweenmagnetic structure 20 and circuit breaker mechanism set forth in Figuresl and 3 is meant to be for illustrative purposes only, and is schematicin nature. Obviously, the type magnetic latch set forth in Figure 1could be applied to any desired type of circuit breaker mechanismwherein the armature 22 would normally control the position of thecircuit breaker cooperating contacts. Furthermore, trip free typemechanism and any other type desired mechanism could be interposed oradded to the connection between the armature 22 and the circuit breakerContact structure.

It has been found in the past that when utilizing the type of magneticstructure set forth in Figures l, 2 and 3 that the armature 22 will bereleased from the magnetic structure 20 responsive to relatively rapidincreases in current or decreases in current. Thus, in the case ofFigure 4 which shows a first, second and third rectifier 56, 58 and 60respectively connected in parallel to feed a common load 73 andrectifier 60 is subjected to backtire, then the magnetic latchmechanisms 62 and 64 of circuit breakers 66 and 68 respectively will seea rapid increase in current since they will now feed current into theshort circuited unit 60. By way of example, Figure 5 shows thiscondition for either of units 56 or 58 where at time t1 the unit 60 isfaulted and the current rises from magnitude I1 to I2 in the timeinterval t2 minus t1. This rise in current through the trip units 62 and64 which are here assumed to be of the type set forth in Figures l, 2and 3 has in the past caused a tripping of their associated breakers 66and 68 respectively by a release of their armature members.

Thus, while the faulted unit 60 is removed from the line due to thenormal reverse current trip action of circuit breaker 70 as initiated bymagnetic trip unit 72, the load 62 is completely taken out of service inView of the disconnection of rectiers 56 and 58.

As will be set forth hereinafter, our novel compensating means willoperate on the magnetic trip structure tin such -a manner that lacompensating flux will be introduced `into the magnetic structureresponsive to an increase in current o-f the Itype set forth in Figure 4between the time limits t1 and t2.

It has been further found that if rectiflers 56 and 58 of Figure 4 arenormally carrying the excessively high current I2 and the rectifier,such as rectifier 60, after having its fault corrected is returned .tothe line so as to cause a relatively rapid decrease in current I2 to thecurrent I1 Ain the time t3 minus t4 (Figure 5), once again the ltxripunits 62 and 64 Will operate to open the breakers 66 .and 68 and onceagain remove the rectiers 56 and 58 respectively from the line. Hereagain, however, our novel compensating means may be adapted so asprevent this undesired condition.

The general principles of our novel invention may be understood byreference to Figure 6 which shows the magnetic structure of Figures l, 2`and 3 when adapted with our novel transformer compensating means.Figure 6 shows our novel transformer compensating means, or a feed-backmeans, as being comprised of the transformer means 74 which includes amagnetic core 76 having the bucking bar 36 as a primary winding andsecondary winding 78. The output of the secondary winding 78 isconnected to van auxiliary winding 80 wound'on the magnetic structure 20of the magnetic trip unit. If desired, .a rectifier 82 may be connectedin the output of secondary winding 78, or as is indicated by the dottedlines, the connection may be ra direct one as will be describedhereinafter.

The connection shown in Figure 6 fis specifically directed to aconnection for adding a compensating flux to the magnetic structure 20responsive to a rapid increase in current through the bucking bar 36 asshown Ibetween time t1 to time t2 of Figure 4. As has been describedhereinbefore, a rapid increase in this current for some reason decreasesthe ux linkages between the magnetic structure 20 and the armature 22 soas to allow the 'armature 22 -to be moved to a disengaged position withrespect to structure 20.

In the structure of Figure 6, however, transformer 74 is energizedresponsive to this rapid increase in current through bucking bar 36 soas to induce a voltage across winding 78, which voltage is subsequentlyimpressed upon winding 80 to induce a compensating flux in core 20. Thiscompensating flux then compensates for ythe decreased flux linkagesbetween magnetic structure 20 and armature 22 and prevents operation ofthe tnip umt.

It has Abeen found desirable to construct core 76 in such .a manner thatit would be maintained unsaturated throughout a predetermined currentchange interval, although it is possible to utilize normal currenttransformers for this purpose.

The purpose of rectiier 82 is to prevent energization of coil 80 bysecondary Winding 76 when the current through bucking bar or currentcarrying means 76 decreases from a predetermined value. For with thiscondition, the flux in coil 80 will be in a direction to buck down :theflux through armature 22 and thereby allowv release of the armaturemember. This condition would be undesirable when the current in thebucking bar 36 is being reduced from -an excessively high value to arelatively low value as the reduction in current from value I2 and I1between times t3 and f4 of Figure 5.

However, this conditioncould be extremely desirable during reversecurrent conditions, since the ux induced in coil 80 will aid thereversed flux due to the buckingbar 36S'to buck down the iluxthrough-armature 22' due tothe polarizingcoil 30, and' thereby causefaster operation off the trip unit.

Thus, the rectifier 82 could belaincluded in the circuit depending uponparticular applicationV of: the magnetic trip-unit. That bis, when. itis not necessary to` prevent operation of the magnetic latch'` duringdecrease ofcurrenti from` an excessively high value to al'ower value,then the exclusionof' rectifier 82f would' serve to increase the speedof# magnetic latchunit.

Figure 7 shows the manner in which the magnetic latch unit could beadapted toV compensate lfor conditions of both. increase and `decreaseof current in` the bucking lbar 36. .andi comprises the components ofFigure 6-which operate inthe same manner as described above for rapidincreaseof current plus an additional compensating transformer 84 whichhas a secondary windingl 86.

During a decrease in current from anw excessively high value, secondarywinding 86. connected! in series withv rectier. 88; and magnetic coreWindingy 90l willinduce a. compensating iiux in the proper direction inthe magnetic structure responsive toa decrease in currentin the buckingbar 36.

AsA will; be apparent' to those 'skilled' -in the art coils 7.8-` and86Ucould be mounted on the same magnetic structure 74; the twoindependent magnetic structures being shown. in Figure Tfor illustrativepurposes only.

While each of'Figures 6.and7 have shown our novel transformercompensating means as having a separateV and independent magnetic core,Figure 8 shows a= manner in! which the magnetic structure of: themagnetic trip unit may be utilized as the magnetic core of" thecompensating transformer.

Referring now to Figure 8, -it isseen that a compensating winding orsecondary winding 92 is` wound' on Figure 8 then shows the outputsecondary winding 92.Y as being applied directly across the polarizingWinding 3,0 inV series. with the rectier. 94 so that compensating iluxisinduced into vthe magnetic structure responsive :to `a change lincurrent: in the bucking bar 3,6'r in. theysamemanner `as theembodimentVof Figure 6.

Itis to be noted that. the polarizing coil 301 is now used. to serveboth as a polarizing coil aswell as an auxiliary coil to receive thecompensating signal pulse. It ishoWever, necessary to provide a diodemeans 96 in the polarizing circuit. so as to prevent short circuiting ofthe pulse through the voltage source ofpolarizingv potential. Clearly,the same structure could have been set forth in Figures 6 and 7 Where inFigure 6y the output of secondary winding78could have been applieddirectly tothe polarizing coil 30, rather than to the auxiliary coil80.4

While Figure 8 speciiically shows the circuit connection as includingrectier 94f for allowing passage of a compensatingipulse only whencurrent through the bucking bar. 36 increasesfrom a predetermined valueas seen in Figure 5., Figure 9A shows the manner in which the circuit ofFigure 8 could be modifiedl to provide compensation for both an increasein current through the bucking bar. 36 and a decrease in current throughthe bucking bar 36. In this case, the secondary winding is-comprised oftwo halves 98 and 100'ofy a center tapped coil wound on the highreluctance leg 26 Where Winding-portion 98 is connected to polarizingcoil 301through the rectier 94and serves thefsame purpose asy didsecondary winding 92 of1Figure8.

Winding portion 100, however, which is connected through the rectifier102 will induce a compensating voltage into winding 301'esponsive to aldecrease incurrent through bucking bar 36 from a predetermined valuewhich is excessively high to a lower Value as between the times t3 andt4 of Figure 5 While our novel compensating or feed-back means has beenset forth in Figures 6, 7, 8 and` 9 in conjunction with the magneticstructure of the type setforth in Figures l, 2 and 3, it is to beclearly understood thatI our novel invention could now be applied to awide variety of magnetic structures.

By way of example, the magnetic structure'couldl take the form set forthin Figure 10 wherein an armature 106 is scalable to the armature fluxpath 108; The' armature flux path 108 carries ilux due to the polarizingcoil 110 which is wound on the polarizing luxpathl 112 and the buckingbar 114 which circulates its flux to armature liux path 108 through thehigh reluctance magnetic structure 116.

In the case of the structure of Figure 10 and assuming the bucking bar114 carries current in a normal forward direction, the ux due to thepolarizing coil' 110 and the bucking bar 114 owing through the armatureilux path 108 will flow in the same direction. The ux in the polarizingiluxpath 11'2A will be that due only to the polarizing coil 110, whilethe ux iiowing in high reluctance structure 116` will be that due to thepolarizing flux and bucking bar flux flowing in opposing directions.

It is to be further noted that the armature flux path 108 as seen inFigures 10 and 11 is comprised' of a plurality of horizontally stackedlaminations and has air gaps 118, 120 and 122 extending thereacross.

The armature 106, as is best seen in Figure 12, is composed ofalternating magnetic and non-magnetic laminations which are fastenedtogether in any desired manner. The magnetic portions 128 and 130 and132' are then positionedto straddle the air gaps 118, 120 and 122 of thearmature flux path 108, as best seen in Figure 10.` By this type ofconstruction the flux linking the armature flux carrying structure 108and the armature 106 must rst enter magnetic portion 128 of armature106, and is thereafter turned into the magnetic structure 108 because ofthe non-magnetic portion 124, and after passing non-magnetic portion124, re-enters the armature and then leaves the armature 106 afterpassing slot. 120'andso on.

Hence, for the particular structure set forth in Figures 10, 1l and l2,the ux linking the armature ux path 108 andthe armature 106 enters andleaves the armature 106 six times to thereby effectively increase thenumber of flux linkages between the magnetic structure and its armature,and thus provide a substantially higher holding force for apredetermined amount of magnetic llux.

Furthermore, once the armature 106 is slightly separated from thearmature path 106 the effective air gap will be six times the normalphysical air gap, thus increasing the speed at which the armature isreleased from the magnetic structure.

In the case of the embodiment of Figures 10, l1 and 12, it is clear thatan auxiliary winding 136 would be added on the polarizing structure 112,this Winding being energized in a manner set forth in Figure 6 for acase of compensating Winding 80. A still further winding coil be addedto the structure of Figure l0 for receiving another winding similar towinding 90 of Figure 7.

If, however, it is desired to utilize the structure set forth in Figures8v and 9 wherein the latch magnetic structure is utilized as thetransformer iron of the compensating transformer, then the secondarywinding could be positioned on the high reluctance structure 116, thissecondary winding being seen in Figure l() as secondary winding 138. Inthis case, secondary winding 138 will be connected to a compensatingwinding such as winding 136 for achieving any desired compensation, ashas been set forth hereinbefore.

More specifically, the compensating transformer in this case wouldinclude the high reluctance path 116, armature path 108 and armature106. The primary winding would be the bucking bar or current carryingmember 114, and the secondary winding, of course, is the winding 138. f

Although we have described preferred embodiments of our novel invention,many Ivariations and modifications will now be obvious to those skilledin the art, and we prefer therefore to be limited not by the speciiicdisclosure herein but only by the appended claims.

We claim:

l. A magnetic latch for D.C. circuit breakers; said magnetic latchcomprising a magnetic core and an armature movable into and out ofmagnetic engagement with respect to said magnetic core; said armaturebeing operatively connected to a movable contact of a pair ofcooperating contacts of said D.-C. circuit breaker; Vsaid movablecontact being normally maintained in engagement with its cooperatingcontact by said armature when said armature is in said engagement withsaid magnetic core, said movable contact being movable to a disengagedposition with respect to said magnetic core when said armature is movedout of said engagement with said magnetic core; current carrying meanscarrying at least a portion of the load current of said D.C. breakerpositioned to induce flux linkages between said magnetic core and saidarmature to maintain said armature engaged to magnetic core when saidcurrent flows in a forward direction and polarizing means associatedwith said magnetic core for inducing polarizing ux linkages in the samedirection as said ux linkages due to said current carrying means;reversal of current through said current carrying means causing adecrease in flux linkages between said armature and said magnet coreyto'allow said armature to'be moved to said disengaged positionfwithrespect to said magnet core; and feed-back means including transformermeans connected to be energized responsive to a change in currentthrough said current carrying means, said transformer means beingfurther connected to induce compensating flux linkages between saidmagnet core and said armature responsive to variation in the current ofsaid current carrying means in an increasing direction; said feed-backmeans including diode means therein for blocking operation of saidtransformer means when said current of said current carrying meansvaries in a decreasing direction.

2. A magnetic latch for D.C. circuit breakers; said magnetic latchcomprising a magnetic core and an armature movable into and out ofmagnetic engagement with respect to said magnetic core; said armaturebeing operatively connected to a movable contact of a pair ofcooperating contacts of said D.C. circuit breaker; said movable contactbeing normally maintained in engagement with its cooperating contact bysaid armature when said armature is in said engagement with saidmagnetic core, said movable contact being movable to a disengagedposition with respect to said magnetic core when said armature is movedout of said engagement with said magnetic core; current carrying meanscarrying at least a portion of the load current of said D.C. breakerpositioned to induce ilux linkages between said magnetic core and saidarmature to maintain said armature engaged to magnetic core when saidcurrent flows in a forward direction and polarizing means associatedwith said magnetic core for inducing polarizing flux linkages in thesame direction as said flux linkages due to said current carrying means;reversal of current through said current carrying means causing adecrease in flux linkages between said armature and said magnet core toallow said armature to be moved to said disengaged position with respectto said magnet core; and feed-back means including transformer meanshaving said current carrying means as a primary winding, saidtransformer means having a secondary winding connected to inducecompensating flux linkages between said magnet core and said armatureresponsive to variation in the current of said current carrying means inan increasing direction; said feed-back means including diode meanstherein for blocking operation ,of said transformer means when saidcurrent of said current carrying means varies in a decreasing direction.

3. A magnetic latch for D.C. circuit breakers; said magnetic latchcomprising a magnetic core and an armature movable into and out ofmagnetic engagement with respect to said magnetic core; said armaturebeing operatively connected to a movable contact of a pair ofcooperating contacts of said D.C. circuit breaker; said movable contactbeing normally maintained in engagement with its cooperating contact bysaid armature when said armature is in said engagement with saidmagnetic core, said movable contact being movable to a disengagedposition with respect to said magnetic core when said armature is movedout of said engagement with said magnetic core; current carrying meanscarrying at least a portion of the load current of said D.C. breakerpositioned to induce iiux linkages between said magnetic core and saidarmature to maintain said armature engaged to magnetic core when saidcurrent flows in a forward direction and polarizing means associatedwith said magnetic core for inducing polarizing flux linkages in thesame direction as said flux linkages due to said current carrying means;reversal of current through said current carrying means causing adecrease in flux linkages between said armature and said magnet core toallow said armature to be moved to said disengaged position with respectto said magnet core; and feed-back means including transformer meanshaving said current carrying means as a primary winding, saidtransformer means having a secondary winding connected to inducecompensating flux linkages between said magnet core and said armatureresponsive to variation in the forward current of said current carryingmeans; and rectifier means connected in said secondary winding toprevent induction of compensating iiux in said magnet core when saidvariation in current is in a predetermined direction; said feed-backmeans further including diode means to prevent operation of saidtransformer means when the variation of current is in a directionopposite to said predetermined direction.

4. A magnetic latch for D.C. circuit breakers; said magnetic latchcomprising a magnetic core and an armature movable into and out ofmagnetic engagement with respect to said magnetic core; said armaturebeing operatively connected to a movable contact of a pair ofcooperating contacts of said D.C. circuit breaker; said movable contactbeing normally maintained in engagement with its cooperating contact bysaid armature when said armature is in said engagement with saidmagnetic core, said movable contact being movable to a disengagedposition with respect to said magnetic core when said armature is movedout of said engagement with said magnetic core; current carrying meanscarrying at least a portion of the load current of said D.C. breakerpositioned to induce flux linkages between said magnetic core and saidarmature to maintain said armature engaged to magnetic core when saidcurrent flows in a forward direction and polarizing means associatedwith said magnetic core for inducing polarizing liux linkages n the samedirection as said flux linkages due to said current carrying means;reversal of current through said current carrying means causing adecrease in flux linkages between said armature and said magnet core toallow said armature to be moved to said disengaged position with respectto said magnet core; and feed-back means comprising a first and secondtransformer; each of said first and second transformers having saidcurrent carrying means as a primary winding; each of said first andsecond transformer means having secondary windings connected to induceasoman compensating hun linkages between saidi magnet core andi saidarmature responsive to. an increase: from: a` predetermined value andadecreasefrom an excessively.- high value respectively of. currentthrough said? current carrying means, each of said irst and secondltransformer secondary windings having rectilier means associatedtherewith for preventing induction of compensating flux' responsivetodecrease' of current from saidi excessively-high value and increase ofcurrent from` said predetermined value respectively.-

Al magnetic latch for D.C. circuit breakers; said magnetic latchvcomprising a magnetic core and an armature movable into and out ofmagnetic engagement with respect tosaid magnetic core; said armaturebeingloperatively connectediftd a movable contact of al pair ofcooperating contacts ofsaidI D.C. circuit breaker; said movable contactbeing normally maintainedin engagement with its cooperating contact bysaid armature when said armature isin said engagement with'- saidmagnetic core, saidmovable contact being movable tovadisengaged positionwith respect to said-magnetic core when said armature is moved out ofsaid engagement with said magnetic core; current carrying means carryingat least a portion ofthe load curr-ent of said DL-C.' breaker positionedtoinduce fluxl linkages betweenI said? magnetic core andi said armaturetomaintain saidl armature engaged to magnetic core when said cur-rentflows in a forward direction and polarizing means associated with saidmagneticcore for inducingl polarizing ilux linkages in the samedirectionas said ux. linkages due to said current carrying means;reversal of! current through said currentcarrying means causing adecrease in flux linkagesbetween said armature and; said magnet core toallow said armature to be movedI to said disengaged position-withrespect to said magnet core; and feed-backmeans including transformermeans having said current carrying means as a primary winding, saidtransformer means having a secondary` winding. connected to` inducecompensating` liux linkages between said magnet core and saidarmatureresponsive to an increasey in the current of' said current carryingymeans in an increasingdirection; said eedeback means including diodemeans therein for blocking-'Opern tion of said transformermeans-whensaid current of said currents carrying means var-ies in adecreasing direction;

6. In' az magneticv structure forsealing an armature; said magneticVstructure: havingv magnetic iiuxl induced therein in linkingrelationship with'- respect` tosaidi armature by a irst andsecondlwinding, saidiir-st and! second windings creating flux` in thesame directionl for linking said armaturey and: magnetic structure when=current in said first winding is. in a irst direction and' inA oppositedirections-whenI current in-saidirst winding-is in asecond direction; acompensating means for compensating for a changein iluxlinkages betweengsaid armature: and said magnetic structure whenl saidcurrent insaidfir-stf winding varies,A said' compensating meanscomprisingatransformer: having a primaryv winding and' a secondary winding,v saidVprimary-winding: being connectedto conduct at leastt a. portionof thecurrent' in said! first winding, said secondaryl winding beingAconnected to induce compensating luxin: saidmagnetic structureresponsiveto variation of current: in saidprimary windingv in anincreasing directionggsaidl secondary winding having a diode connectedtherein; said: diode preventing operation or said*compensating'meanswhen said variation ofcurrent in said primary windingis in adecreasingdirection.

7.11m; a magnetic structure for sealingI an armature; said: magneticVstructure having magneticflux induced therein in linking relationshipwithrespect tov said armatureby a=` iirstf and: secondiwinding, saidlirst` and second windings creating; iiuX in; the same direction forlinking said armature and magnetic; structure when. current in saidiirst windinglisin-a firsts directionaand:inaopposite diev rections.when: currentzinsaid rst winding isdn: asecond directiong; alcompensating; means for compensating for a change: influx linkagesbetween said armature-and said' magnetic: structure when said currentin? said iirsr winding varies, said compensating means comprising; a:transformen havingx a primary,y winding and'` ai secondary winding,sai-df primary Winding being. connectedto conduct at leash a portiona ofthe: current in' said" irst winding, Vsaid secondaryl winding: beingconnected to induce compensatr ingun in said magnetic structureresponsivey toi variation of current in said primary winding in-.anincreasing direction;V said secondary winding having a diode connectedtherein; said diode preventing operation of said compensating. meanswhensaid variation of currentinsaid` primary winding' is in aidecreasing direction;` said transformer being constructed to'bemaintainedunsaturated over a predetermined range of variationofcurrent in said primary winding. y

8. Ina magnetic structure for sealing anl armature; said magneticstructure` having magnetic uX induced therein inlinkingl relationshipwith respect tov said armature by a first and second winding, said iirstand second windings creatingv flux in the same direction for linkingsaid armature and magnetic structure whencurrent inV said rst Windingis; ini a rst directionand in opposite directions-,when current` in saidrst winding is in asecond direction; a compensating means forcompensating for a changein flux linkages betweensaid armature and saidmagnetic structure when-*said current in said iirstawinding varies, saidcompensating means comprisingl a transformer having a primary windingand asecondary winding, saidprimary winding being connected to conductat leastv a portion ofthe current in said irst winding, saidsecondary'windingbeingr connected to induce compensate ing fluir` insaidmagnetic structure responsivetol variation of current inzsaid: primarywindinggsaid transformer be'- ing constructed tobe maintainedunsaturated over apredetermined range of variation of current! in saidprimary winding, and rectifier means connected in said secondary windingto prevent induction of said compensating ux when said currentin saidprimary winding varies ina predetermined direction;

9. `Ina magnetic structure for sealing an armature; said magneticstructure comprising; an armature iiux path,y aA polarizing iiux pathand, ahigh'reluctance path; polarizing means wound on: said polarizingpath for inducing unidirectionall flux insaid armature path and buckingbar means for inducing flux-insaid armature path-inthe Same. direction.as that due to said polarizing meanswhen current insaid buckingbar isinthe same direction; said high reluctance pathbeing'positionedwithrespect to said polare izing means and said buckingbar means to carry their said uxes in: opposing/directions; acompensating coil wound on said highreluctance ux path; saidcompensating coil being energized responsive, to Variations in thevcurrent of said.bucking;bar;lsaid compensating coil being connectedto-induce. compensating flux; in said' armature path responsive tovariations in current' of saidbucking bar in an-increasing direction;saidcompensatingfcoil hav` inga diode connected therein to prevent'operation of said compensating means when said variation of current insaid bucking. bar is in: a: decreasing directiona l0. In a magneticstructure for sealing an armature; said. magnetic. structure comprisingan t armature: flux path', a polarizing hun path and athighreluctancepathg; polar*- izingmeansiwound on said polarizingpath forinducing unidirectionallnxin saidarmature path and bucking bar means-forinducing ux insaid armature path in the. same direction asf thatduetosaid' polarizingmeans when current insaidbucking bar is in the: samedirectionysaid' high reluctancey path: being positioned with respecttosaid polarizing, means andY said: bucking barl means to carry theirsaid fluxes int opposing direction;- a compensating coil wound oni said:high; reluctance flux path; said conrpensating coil: being energizedresponsive -to variations in the` currentl off-'saidl bucking' har;lsaid compensating coil beingconnectedto induce compensating iuxl in'said arrna' 13 ture path responsive to variations in current of saidbucking bar; the output of said compensating coil being rectiiied toprovide compensation ux only when said current variation in said buckingbar is in a predetermined direction.

11. In a magnetic structure for sealing an armature; said magneticstructure comprising an armature flux path, a polarizing flux path and ahigh reluctance path; polarizing means Wound on said polarizing path forinducing unidirectional flux in said armature path and bucking bar meansfor inducing ux in said armature path in the same direction as that dueto said polarizing means when current in said bucking bar is in the samedirection; said high reluctance path being positioned with respect tosaid polarizing means and said bucking bar means to carry their saiduxes in opposing direction; a rst and second compensating coil Wound onsaid high reluctance ux path; said rst and second compensating coilbeing energized responsive to variations in the current of said buckingbar; said rst compensation coil causing induced compensating ftux insaid armature path only when said bucking bar current increases, saidsecond compensation coil causing induced compensating ux in saidarmature path only when said bucking bar current decreases from anexcessively high value.

References Cited in the le ot this patent UNITED STATES PATENTS1,787,931 Besold Jan. 6, 1931 1,920,745 Grunholz Aug. 1, 1933 2,672,584Rolf Mar. 16, 1954

